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 @new--To make sure we are on the same page, yes there is 1/2 the _area_ on an APS-C sensor because each side is 2/3 as long--thus the 1.5 "crop factor" (the reciprocal of 2/3 is 3/2 or 1.5)

I can't agree with your blanket statement that older Nikon glass works "great" on FX cameras. Many of those lenses have substantial light fall off when used with FX (for example my beloved 70-200 AF-S--which is one big reason Nikon has come up with a newer and unfortunately more expensive version). That fall off may not bother you, but it does bother many photographers and therefore can not be ignored.